This is the third book in the Song of the Lioness quartet.
The back of the book says:
A knight at last...
Alanna of Trebond heads out to seek adventure in the desert of Tortall. Captured by desert tribemen, she is forced to prove herself in a magical duel. But a real challenge doesn't come until after she wins. As the first female shaman, Alanna must fight the ancient traditions of the tribes- for their own sake and for the sake of all of Tortall. This third book in the Song of the Lioness, continues Alanna's saga, and she strikes out alone and sdiscovers herself anew.